1. Field of the Invention
The present invention relates to an image sensor and, more particularly, to an image sensor having a plurality of output channels.
2. Description of the Related Art
These days, image sensors for digital cameras make remarkable progress and are rapidly gaining a larger number of pixels for higher resolution of still images. Along with this, it is an urgent issue to increase the pixel signal readout speed in order to ensure sequential shooting performance necessary for a camera. Japanese Patent Laid-Open No. 2005-286933 discloses a CCD image sensor which parallely reads out pixel signals through a plurality of column shift registers to increase the readout speed.
A digital camera can capture still images, and even moving images. The digital camera generally uses one image sensor to capture both still and moving images. The image sensor requires high resolution for still images, and requires a high frame rate for moving images while decreasing the resolution to match a general moving image standard. Japanese Patent Laid-Open No. 2005-130382 discloses an image sensor which adds pixel signals to decrease the resolution and increase the frame rate.
The CCD image sensor disclosed in Japanese Patent Laid-Open No. 2005-286933 parallely reads out pixel signals through a plurality of output column shift registers. Thus, the apparent signal readout speed is higher than in readout through a single output column shift register. However, Japanese Patent Laid-Open No. 2005-286933 does not describe any idea of increasing the frame rate used in capturing a moving image from that used in capturing a still image.
The image sensor disclosed in Japanese Patent Laid-Open No. 2005-130382 adds pixel signals by merging charges on a horizontal output line. However, Japanese Patent Laid-Open No. 2005-130382 does not describe any concept of parallely outputting sums through a plurality of channels.
That is, Japanese Patent Laid-Open Nos. 2005-286933 and 2005-130382 do not have any idea of increasing the frame rate by parallely reading out low-resolution pixel signals through a plurality of channels in capturing a moving image.
Low-resolution pixel signals may be parallely read out through a plurality of channels by simply assigning them to the plurality of channels. However, this puts a load on the process of a processing circuit which processes the pixel signals. For example, to execute a process common to that in full pixel readout, the processing circuit must rearrange the order of received low-resolution pixel signals.